1. Field of the Invention
The present invention relates to a brake system of a vehicle such as an automobile, and more particularly, to a brake system of a hybrid type vehicle equipped with an internal combustion engine and a motor-generator as drive power means thereof.
2. Description of the Prior Art
The hybrid type vehicles are spotlighted in these years under the apprehension of the fuel resource exhaustion and the atmospheric pollution. In the hybrid type vehicles currently under developments, a motor-generator is incorporated so as to operate as a motor for driving the vehicle when supplied with an electric current from a battery and as a generator for charging the battery when driven by the kinetic energy of the vehicle. It is generally at the time of braking the vehicle that the motor-generator is operated as the generator.
In an aspect of driving four-wheeled vehicles for various desired performances, it will not always be desired that the front and rear wheels are both driven or equally driven, as the rear drive cars or the front drive cars are really quite common, while in an aspect of regenerating as much an electric energy as possible from the kinetic energy of four-wheeled vehicles during the braking thereof, it will generally be desired that the front and rear wheels are both equipped with the regeneration brakes.
On the other hand, in the motor-generators for use with the hybrid type vehicles, the balance between the performance or efficiency in operation as a motor and the performance or efficiency in operation as a generator will widely change according to the design and/or size or capacity thereof.
In view of the above, it is expected that, when separate motor-generators are provided for a pair of front wheels and a pair of rear wheels in a hybrid type vehicle, the regeneration efficiency of the motor-generator for the front wheels and that of the motor-generator for the rear wheels are substantially different from one another according to various designs of the hybrid type vehicles with regard to the driving performance thereof. Much greater will be such a difference when a motor-generator is provided only for a pair of front or rear wheels, while for the other pair of rear or front wheels a mere regeneration brake is provided, because, when the regeneration brake is provided in the form of a motor-generator, the basic assembly of the rotor and the stator is used in common for the motor function and the generator function, and therefore, such a dual function assembly may be designed and manufactured for a higher performance even at a higher manufacturing cost, so that it shows a substantially higher regeneration efficiency than a mere regeneration brake.
In consideration of such a diversity, or diverse probability, in the design and manufacture of the regeneration brakes of the hybrid type vehicles with regard to the regeneration efficiency thereof, it is a primary object of the present invention to provide an improved brake system of a hybrid type vehicle having regeneration brakes for the front and rear wheels, wherein the front and rear regeneration brakes are effectively operated to regenerate as much an amount of electric energy from the kinetic energy of the vehicle as possible during the braking thereof.
According to the present invention, the above-mentioned primary object is accomplished by a brake system of a hybrid type vehicle having a pair of front wheels and a pair of rear wheels, comprising:
front regeneration brake means for selectively braking the front wheels with a regeneration of an electric energy from a kinetic energy of the vehicle at a first regeneration efficiency;
rear regeneration brake means for selectively braking the rear wheels with a regeneration of an electric energy from the kinetic energy of the vehicle at a second regeneration efficiency different from the first regeneration efficiency;
front friction brake means for selectively braking the front wheels;
rear friction brake means for selectively braking the rear wheels; and
control means for operating the front and rear regeneration brake means and the front and rear friction brake means such that, when the vehicle is braked at a controlled braking force, either of the front and rear regeneration brake means working at a higher regeneration efficiency than the other apply as much a braking force to the corresponding front or rear wheels as available thereby for the controlled braking force under a condition that a ratio of a braking force applied to the rear wheels to a braking force applied to the front wheels is not larger than a value predetermined therefor, with a remainder of the controlled braking force, if any, being applied by at least one of the other of the front and rear regeneration brake means and the front and rear friction brake means.
In more detail, when the first regeneration efficiency of the front regeneration brake means is higher than the second regeneration efficiency of the rear regeneration brake means, the brake system according to the present invention may be so adapted that the front regeneration brake means apply such a braking force to the front wheels that is the lower of the controlled braking force and a maximum regeneration braking force available thereby, and when the remainder of the controlled braking force is totally applicable to the rear wheels under the condition that the rear/front braking ratio is not larger than the predetermined value, the rear regeneration brake means apply as much a braking force to the rear wheels as available thereby, with a further remainder of the controlled braking force, if any, being applied by at least the front friction brake means to the front wheels.
In such a brake system, the further remainder of the controlled braking force may be applied only to the front wheels by the front friction brake means.
Or, alternatively, in such a brake system, the further remainder of the controlled braking force may be applied to the front and rear wheels by the front and rear friction brake means, respectively, at a ratio such as a front share of the controlled braking force according to the predetermined value of the rear/front braking ratio minus the maximum regeneration braking force available by the front regeneration brake means vs. a rear share of the controlled braking force according to the predetermined value of the rear/front braking ratio minus a maximum regeneration braking force available by the rear regeneration brake means.
According to another detail, when the first regeneration efficiency of the front regeneration brake means is higher than the second regeneration efficiency of the rear regeneration brake means, the front regeneration brake means apply such a braking force to the front wheels that is the lower of the controlled braking force and a maximum braking force available thereby, and when the remainder of the controlled braking force is not totally applicable to the rear wheels under the condition that the rear/front braking ratio is not larger than the predetermined value, the brake system may be so adapted that the front friction brake means apply such a braking force to the front wheels that corresponds to a difference between a front share of the controlled braking force according to the predetermined value of the rear/front braking ratio and the braking force applied to the front wheels by the front regeneration bake means, while the rear regeneration brake means apply as much of a rear share of the controlled braking force according to the predetermined value of the rear/front braking ratio as available thereby to the rear wheels, with a further remainder of the controlled braking force, if any, being applied to the rear wheels by the rear friction brake means.
According to still another detail, when the second regeneration efficiency of the rear regeneration brake means is higher than the first regeneration efficiency of the front regeneration brake means, the rear regeneration brake means may apply as much of a rear share of the controlled braking force according to the predetermined value of the rear/front braking ratio as available thereby to the rear wheels, while the front regeneration brake means may apply as much of a remainder of the controlled braking force as available thereby to the front wheels, with a further remainder of the controlled braking force, if any, being applied by at least the front friction brake means to the front wheels.
In such a brake system, the further remainder may be applied by only the front friction brake means to the front wheels.
Or, alternatively, the further remainder may be applied by the front and rear friction brake means to the front and rear wheels, respectively, at a ratio such as a front share of the controlled braking force according to the predetermined value of the rear/front braking ratio minus a maximum regeneration braking force available by the front regeneration brake means vs. the rear share of the controlled braking force according to the predetermined value of the rear/front braking ratio minus a maximum regeneration braking force available by the rear regeneration brake means.